For the dressing:
Slice the tomatoes and arrange them on a serving plate.
Scatter with the onion slices and set aside.
at this stage you can season the tomatoes with a couple of pinches of salt.
Salt will make the tomatoes release some juices that blend beautifully with the dressing.
In a bowl whisk all the ingredients for the dressing (apart from the garlic) until fully combined.
Add the garlic, season with salt and pepper. Leave it for a couple of minutes ( so the dressing will absorb some garlic flavour).
Now pour the dressing over the tomatoes. You can leave the salad to marinate for about 30 minutes, but not for longer as the tomatoes will start to loose their shape.
Scatter torn basil or parsley leaves to garnish.